The Transgenic Animal Core will provide investigators in the three Projects with uniformly maintained, specific-pathogen-free colonies of aging knockout/transgenic mice with alterations in genes coding for either Mn-superoxide dismutase (Sod2) or Cu/Zn-superoxide dismutase (Sod1). In addition, the Transgenic Animal Core will generate conditional knockout mice for Sod2 in which the skeletal muscle is null for MnSOD (Sod2D3-/- mice). The following knockout/transgenic mouse models and their wild type littermates will be maintained in the Transgenic Animal Core: 1) MnSOD heterozygous (Sod2+/-), knockout mice, 2) MnSOD conditional homozygous (Sod2D3-/-) knockout mice, 3) transgenic mice over-expressing MnSOD (SodTg+/o), and 4) Cu/ZnSOD heterozygous (Sod1+/-) and homozygous (Sod1-/-) mice. The specific aims of the Transgenic Animal Core are as follows: 1. To produce conditional knockout mice (Sod2D3-/-) that do not express MnSOD in skeletal muscle. 2. To maintain breeding colonies of the transgenic mice to produce female knockout/transgenic mice used in this study by the three Projects. 3. To maintain aging colonies of female knockout/transgenic and wild type control mice. Animals from these colonies will be used by the investigators in three Projects for the experiments described in this proposal.